Project 4: Vaccines and antibiotics help prevent or ameliorate many infectious diseases. Yet, natural evolution and engineering for bioterrorism purposes create novel biothreats for which novel countermeasures are necessary including i) development of novel chemotherapeutic agents, and ii) utilization of natural defense mechanisms, i.e., the immune system. The latter one may include non-specific activation of the innate immune system and manipulation of the adaptive immunity through vaccines. We now know that vaccines act through dendritic cells (DCs), the initiators and controllers of immune effectors (T and B lymphocytes) differentiation. Just as lymphocytes are composed of different subsets, DCs comprise several subsets that differentially control lymphocyte function. It is therefore important to understand how distinct DC subsets modulate vaccine immunity in vivo. Such knowledge will permit us to design targeted vaccines that will induce a desired type of immunity. This project is designed to i) construct novel human vaccines comprised of antibodies targeting distinct subsets of human DCs coupled to an antigen of choice, either as chemical conjugates or as antibody-antigen fusion proteins, and ii) determine the quality and magnitude of antigen-specific immune responses elicited in vitro and in vivo by targeting distinct subsets of human DCs. We will evaluate, in the mice with a human immune system (Humouse), the induction of specific cellular and humoral immune responses using Influenza virus as a model pathogen. AIM 1 will determine whether anti-DC mAb/Flu conjugates can induce Flu-specific secondary responses in vitro. AIM 2 will determine whether anti-DC mAb/Flu conjugates that target different DC subsets prime immune responses in vitro. AIM 3 will determine the in vivo targeting of human DC subsets by selected anti-DC mAb/Flu conjugates. AIM 4 will determine whether specific anti-DC mAb/Flu conjugates targeted to distinct human DC subsets in vivo permit the priming of Flu-specific protective immune responses. The ultimate parameter of vaccine potency will be the protection of Humouse from virus rechallenge. This study will lead to generation of novel vaccines targeted to human DC subsets in vivo.